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A new strain of H7N9 bird flu has been found in birds and people in China. No ongoing person-to-person spread of this virus has been found at this time. Here are some common questions and answers about this new virus.

What is H7N9?

“H7N9” is the designation for one subtype of influenza viruses that is sometimes found in birds, but that does not normally infect humans. Like all influenza A viruses, there also are different strains of H7N9. Beginning at the end of March 2013, China reported human and bird (poultry) infections with a new strain of H7N9 that is very different from previously seen H7N9 viruses.

Is this new strain of H7N9 infecting humans?

Yes. While H7N9 viruses had never before been detected in people, from March 31 through April 30, 2013, China reported more than 126 cases of human infection with this new H7N9 virus.

How are people getting infected?

This virus has been found in birds (poultry) in China in some of the same areas where human infections have happened. Available evidence suggests that most people have been infected with the virus after having contact with infected poultry or contaminated environments.

How do people get infected with bird flu viruses?

Human infections with bird flu viruses are rare, but have happened in the past, usually after close contact with infected birds (both live and dead) or environments contaminated with bird flu virus.

Infected birds can shed a lot of flu virus, for example, in their droppings or their mucus. If someone touches an infected bird or an environment contaminated with virus and then touches their eyes, nose or mouth, they may be infected with bird flu virus. There is some evidence that infection may also occur if the flu virus becomes airborne somehow, such as when an infected bird flaps it wings. If someone were to breathe in airborne virus, it’s possible they could get infected.

Is infection with this virus serious?

Most of the reported cases of human infection with this virus have had very serious illness. There also are reports of some milder illness and one possible report of a person who tested positive for the virus who did not have any symptoms.

What are the symptoms of illness with this virus?

Symptoms have started with high fever and cough. A lot of the cases have progressed to very serious illness, including severe pneumonia, acute respiratory distress syndrome (ARDS), septic shock and multi-organ failure leading to death.

Is this virus spreading from person-to-person?

China has conducted extensive case investigations of people infected with the H7N9 virus and their close contacts and has found no evidence of "sustained" person-to-person spread at this time, which is the kind of ongoing spread that is necessary for a pandemic to occur. However, CDC is aware of a small number of confirmed H7N9 influenza cases in China in which “limited” person-to-person spread of the virus could not be ruled out. "Limited" or "dead end" virus spread usually refers to when a virus from an animal host infects a person and then spreads to a caretaker or close contact of that person but not much further. During April through summer 2013, China’s investigations of people infected with the H7N9 virus were unable to rule out the possibility that limited person-to-person spread may have occurred in five clusters of cases. Based on what we know about other bird flu viruses, some limited person-to-person spread of H7N9 virus is not surprising. Limited person-to-person spread of other bird flu viruses is thought to have occurred rarely in the past, most notably with avian influenza A (H5N1). CDC expects that additional limited person-to-person transmission events with the H7N9 virus could occur in the future if the virus continues to spread between birds and people. CDC and global public health experts are monitoring H7N9 viruses in China for changes that could allow them to spread more easily among people. At this time, no cases of H7N9 virus infection outside of China have been reported, and these viruses have not been detected in people or birds in the United States. CDC does not have any new or special recommendations for the U.S. public at this time regarding H7N9, and the risk to people in the United States remains low.

Is it possible that this virus will spread from person-to-person?

Yes. Based on what we know about human infections with other bird flu viruses, it’s possible and even likely that there will be some limited person-to-person spread with this virus. The important factor will be to determine whether this virus gains the ability to spread easily from one person to another. Sustainable human to human spread is needed for a pandemic to start. Health officials are watching the situation closely for this.

Is there a vaccine to protect against this new H7N9 virus?

No, right now there is no vaccine to protect against this virus. CDC and others are working to develop a vaccine candidate virus that could be used to make a vaccine if it is needed.

Are there medicines to treat illness associated with this virus?

CDC recommends oseltamivir (Tamiflu®) and zanamivir (Relenza®) for treatment of H7N9. Most of the H7N9 viruses that have been studied are likely susceptible (sensitive) to the two influenza antiviral drugs that are used to treat seasonal flu. Those drugs are oseltamivir (Tamiflu®) and zanamivir (Relenza®) (neuraminidase inhibitors). Like seasonal influenza viruses, avian A(H7N9) viruses are resistant to the influenza antiviral drugs known as the adamantanes.

It’s important to note that influenza viruses may acquire genetic changes which can make one or more influenza antiviral drugs less effective. This happens with seasonal influenza viruses and could happen with H7N9 viruses found in China. As new H7N9 virus isolates are received, CDC will conduct ongoing testing to determine the susceptibility of other H7N9 viruses to existing antiviral drugs. More information about antiviral resistance is available at Influenza Antiviral Drug Resistance: Questions & Answers.

What is the risk from this virus in the United States right now?

No cases of human or bird infection with this H7N9 virus have been detected in the United States. At this time, the risk to people in the United States is considered to be low.

Is it possible that human cases of H7N9 flu will be found in the United States?

Yes. The most likely scenario for this right now would be H7N9 infection in a traveler from China. Many people travel between China and the United States. CDC issued a health alert for public health officials and clinicians in the United States to be on the look-out for flu symptoms in travelers who are returning from countries with bird flu. CDC has issued guidance for isolating, testing, and treating such patients. However, since this virus does not seem to be spreading easily from person-to-person, a few cases in the United States with travel links to China would not change the risk of infection for the general public in the United States.

I am a U.S. resident experiencing flu-like symptoms (e.g. coughing, fever, sore throat, etc.). How do I know if I have seasonal influenza, H7N9 influenza, or MERS-CoV (Middle Eastern Respiratory Syndrome Coronavirus)?

Seasonal influenza, H7N9 influenza, or MERS-CoV infection can cause similar respiratory symptoms. However, of these viruses, your symptoms are most likely caused by seasonal influenza. Influenza viruses can still circulate and cause illness even when flu activity is low in the United States. Infection with H7N9 and MERS-CoV are uncommon. Imported cases of MERS have been reported in the United States. All MERS cases have been linked to countries in or near the Arabian Peninsula. The majority of H7N9 infections have occurred in China. No cases of H7N9 have been reported in the United States. At this time, H7N9 has been detected only in China or travelers from China.

If you are hospitalized for a severe respiratory illness of unknown causes within 10 days of traveling to a country where H7N9 has been detected, or you if you have come in contact with a patient who is confirmed to have H7N9 infection, you may be tested for this disease.

For information regarding the signs and symptoms of MERS, and whether you may need to be tested, please review the MERS case definitions.

It is not possible to determine whether a patient has seasonal influenza, H7N9 influenza, and MERS-CoV infection or illness due to another pathogen based on symptoms alone. However, there are tests to detect seasonal influenza, H7N9 influenza, MERS-CoV infection. Your doctor will determine if you should be tested for any of these illnesses based on your symptoms, clinical presentation and recent travel history.

What are the challenges doctors face in identifying and distinguishing between cases of seasonal flu, avian influenza A (H7N9) and MERS-CoV (Middle Eastern Respiratory Syndrome Coronavirus) this season?

Seasonal influenza, H7N9 influenza and MERS-CoV infection can cause similar respiratory symptoms, including fever and cough. However, so far, symptoms of most reported cases of H7N9 and MERS-CoV have been more severe than is common with seasonal influenza. Of these viruses, doctors are most likely to encounter patients with seasonal influenza infection. Seasonal influenza viruses circulate each year in the United States, with most flu activity occurring between October and May.

CDC continues to closely monitor these viruses globally; working with the World Health Organization (WHO) and other partners to understand the risks of these viruses to the public’s health. At this time, H7N9 has only been detected in China or in travelers from China. No cases of H7N9 have been reported in the United States. Cases of MERS-CoV in the United States have only been detected in travelers returning from or near the Arabian Peninsula.

Check the CDC website for the latest guidance and situation updates on these viruses.

How are H7N9 virus infections diagnosed in people?

There are currently no tests available over the counter or at a doctor’s office that can quickly detect and distinguish between the H7N9 virus and other flu viruses. However, a more sophisticated test that specifically detects H7N9 virus has been developed by CDC for use by qualified public health laboratories in the United States and internationally. This test involves collecting a respiratory tract (i.e., nose, throat, lung) sample from a sick patient. The sample is then sent to a public health laboratory where a procedure known as rRT-PCR (real-time reverse transcriptase polymerase chain reaction) is conducted. rRT-PCR is very accurate and sensitive at detecting flu viruses. This procedure typically provides results within 4 hours; however, the time involved in processing and reporting results may vary depending on the laboratory.

Does CDC recommend that people delay or cancel trips to China because of H7N9 flu?

Since H7N9 is not spreading easily from person-to-person at this time, CDC does not recommend that people delay or cancel trips to China. The World Health Organization also is watching this situation closely and does not recommend any travel restrictions.

What advice does CDC have for people traveling to China?

CDC advises travelers to China to take some common sense precautions, like not touching birds or other animals and washing hands often. Poultry and poultry products should be fully cooked. CDC will update its advice for travelers if the situation in China changes. This guidance is available at Avian Flu (H7N9) in China.

Should travelers to China get a prescription for antivirals before their trip?

At this time, CDC does not recommend prescribing antiviral drugs for prevention or self-treatment of H7N9 flu. CDC recommends that travelers to China follow common sense precautions to protect themselves and monitor their health during and after their trip. Anyone with fever, coughing, or shortness of breath within 10 days of traveling to China should see a doctor and tell the doctor about the recent travel to China.

What does CDC advise for people in the United States with regard to H7N9?

CDC does not have any new or special recommendations for the U.S. public at this time regarding H7N9.

Is CDC worried that an H7N9 pandemic will start?

This is a serious public health situation and it’s possible that a pandemic could start if this virus were to change to spread easily between people. CDC is preparing for that possibility.

What is CDC doing in response to H7N9?

CDC is following this situation closely and coordinating with domestic and international partners, including China CDC and the World Health Organization. On April 8, 2013 CDC activated the Emergency Operation Center (EOC) at Level 2 (limited activation) to support the management of the emerging H7N9 situation in China. CDC also is sending a team to China to support the domestic outbreak response.

In addition, CDC is taking routine preparedness measures, including:

Developing a candidate vaccine virus that could be used to make vaccine if it becomes necessary.

Distributing a new test kit developed by CDC that can detect this virus and which can be used by other public health laboratories.

Conducting animal studies to learn more about the severity of disease associated with this virus and how the virus spreads.

Conducting studies on blood samples to see whether there is any existing immunity to this virus in the population.

Conducting ongoing testing to determine H7N9 susceptibility to the licensed influenza antiviral drugs, oseltamivir (commercially known as Tamiflu®) and zanamivir (Relenza®) as well as investigational antiviral drugs.

CDC also is gathering more information to make a more thorough public health risk assessment. This is an evolving situation and there is still much to learn.